1. Technical Field
The present invention generally relates to bacterial corrosion protection in electric submersible pump (ESP) industry. More specifically, the present invention relates to ESP with corrosion preventing coating as well as a method of reducing the content and inhibiting the growth and activity of bacteria, especially sessile bacteria such as sulfate reducing bacteria (SRB) in ESP components.
2. Description of the Related Art
Electrical submersible well pumps for deep wells are normally installed within casing on a string of tubing. Usually the tubing is made up of sections of pipe which are screwed together. The motor is supplied with power through a power cable that is strapped alongside the tubing. The pump is typically located above the motor and connected to the lower end of the tubing. The pump pumps fluid through the tubing to the surface. One type of a pump, a centrifugal pump, uses a large number of stages and is particularly suited for large pumping volume requirements.
For lesser pumping volume requirements, a progressing cavity or PC pump may be employed. PC pumps utilize a helical rotor that is rotated inside an elastomeric stator which has double helical cavities. PC pumps may be surface driven or bottom driven. Surface driven PC pumps have a rod which extends down to the pump in the well, whereas bottom driven PC pumps are driven by electric motors located in the well.
Water flooding is widely used in the petroleum industry to affect the recovery of oil. This process increases the total yield of oil present in a formation beyond what is usually recovered in the primary process. It is desirable in this process to maintain a high rate of water injection with a minimum expenditure of energy. Any impediment to the free entry of water to oil-bearing formations seriously reduces the efficiency of the recovery operation.
Water flooding systems provide an ideal environment for growth and proliferation of biofilms. Large amounts of water are transported through these systems and injected into oil bearing formations in an effort to maintain reservoir pressure or to increase the mobility of oil through the formation to producing wells. The large surface area of the water distribution network encourages biofouling, which is the attachment and growth of bacteria on the pipe walls.
Biofouling caused by anaerobic bacteria is compounded in water floods by the practice of removing oxygen from the water before injection. The removal of oxygen is done to minimize corrosion of equipment; however, the anoxic conditions provide an ideal environment for the growth of sulfate reducing bacteria (SRB) in the biofilms. This phenomenon is observed both on the injection side and producing side of the water flood operation. The metabolic activity of these bacteria can lead to accelerated corrosion rates, plugging of filters, health hazards from the sulfide production, and eventual souring of the formation (a sour well contains hydrogen sulfide).
A common method used to control biofouling in the art is regular application of a biocide. The biocide is generally selected based on its performance in a standard laboratory evaluation test. Glutaraldehyde (pentanedial), which is a highly effective quick-kill biocide, is commonly used to control biofouling. Usually, the biocide is added to the system periodically in predetermined dosage regimes. However, such commonly used method has some disadvantages: it requires large quantity and periodic addition of the biocide, which can increase the cost. Besides, glutaraldehyde is unstable on storage, if not stored properly.
Therefore, there is clearly a need for an improved method to protect electric submersible pump components from microbiologically induced corrosion with long-lasting effect.